The goal of this IPCAVD is to develop an effective AIDS vaccine. Based on recent findings, we are focusing on strategies which will employ primary immunization with DNA vaccines followed by boosting with protein antigens. We have selected SHIV 89.6 as a virus which is well suited for development of experimental vaccines which can be evaluated in primates, and advanced to trials in humans using related approaches. In this project, we will design and produce SHIV protein antigens including virus-like particles and novel soluble protein immunogens, and analyze humoral and cellular immune responses induced by these antigens. We have recently developed approaches for assembly of SIV virus-like particles (VLPs) containing Env and Gag proteins using baculovirus and vaccinia virus based expression systems. In this present proposal, we will develop similar procedures to produce SHIV antigens. The first specific aim is to utilize recombinant expression systems for the production of non-infectious SHIV VLPs and investigate the immune responses to these antigens. We will also determine conditions for the production of SHIV VLPs with deglycosylated Env proteins, which may expose additional antigenic determinants. The immune responses to the glycosylated and de-glycosylated VLPs will be compared in mice and rabbits in collaboration with projects 1 and 3. In our second specific aim, we will design and produce novel SHIV Env protein immunogens which are effective in boosting immune responses to DNA vaccines. We have previously described the production of secreted oligomeric forms of the HIV-1 Env protein by expression of env genes lacking the membrane spanning domain and cytoplasmic tail. Similar approaches will be used to express SHIV Env protein oligomers. In collaboration with Project 1, we will also design and express novel chimeric Env proteins as an approach to enhance the immunogenicity of the purified proteins. Finally, as an approach to enhance the duration of immunity, we will investigate the potential of microencapsulated SHIV antigens for use in systemic boosting following primary immunization with DNA vaccines. This approach has been used successfully to obtain sustained release of systematically administered proteins including vaccine antigens. Immunization strategies which yield optimal results in mice and rabbits will be selected for subsequent evaluation in primates.